Heat-Curable Silicone Rubber Composition For Rubber Laminate

ABSTRACT

A heat-curable silicone rubber composition for a rubber laminate composed of a silicone-rubber layer and a rubber layer of a material other than silicone, the composition comprising: an alkenyl-containing diorganopolysiloxane (A) which comprises: 50 to 99 mass % of a diorganopolysiloxane (A1) that contains alkenyl groups, is capped at molecular terminals with alkenyl-containing organosilyl groups, and is free of alkenyl groups in side molecular chains; 1 to 50 mass % of an alkenyl-containing diorganopolysiloxane (A2) having two or more alkenyl groups in a side molecular chain; a fine silica powder (B); an organohydrogenpolysiloxane (C) having in one molecule at least two silicon-bonded hydrogen atoms; and an organic peroxide (D).

TECHNICAL FIELD

The present invention relates to a heat-curable silicone rubbercomposition for a rubber laminate composed of a silicone rubber layerand a rubber layer of a material other than silicone. Herein, the term“material other than silicone” covers organic synthetic rubber materialssuch as, e.g., fluororubber, acrylic rubber, nitrile rubber, andethylene-propylene rubber.

BACKGROUND ART

Recent improvements in automobile efficiency and fuel-consumption led toincrease of temperature in the automobile engine compartment. As aresult such rubber materials as acrylo-nitrile-butadiene copolymers,hydrogenated acrylo-nitrile-butadiene copolymers, or similaracrylo-nitrile rubbers; acrylic rubbers, copolymers of ethylene andacrylic acid ester, copolymers of acrylic acid ester, ethylene, andvinyl acetate, or similar acrylic rubbers; EPM, EPDM , or similarethylene-propylene rubbers, etc., which are conventionally used formanufacturing parts exposed to high temperatures of the enginecompartment appeared to be insufficient in their resistance to heat. Onthe other hand, silicone rubbers have normally insufficient resistanceto fuel oil and are highly permeable to gases, and therefore their useis limited, especially in areas where they can be exposed to fuel oilsor fuel-oil-vapors.

It was proposed to solve the above problem by forming a rubber laminatefrom silicone rubber and rubber other than silicone rubber. Inparticular, it was proposed to form a silicone laminate body byincorporating a fluororubber, which is characterized by excellentresistance to chemicals and fuel oils. However, since fluororubber haslow surface energy and low reactivity, it is difficult to provide strongbonding between a fluororubber layer and a silicone-rubber layer.Therefore, several studies have been undertaken in order to solve theabove problem.

For example, a method was proposed for simultaneous cross-linking andcuring a non-cross-linked silicone rubber and a non-cross-linkedfluororubber while maintaining both rubbers in mutual contact (seeJapanese Unexamined Patent Application Publication (hereinafter referredto as “Kokai”) 2000-193152). Furthermore, Kokai 2003-19772 discloses arubber laminate obtained by simultaneously vulcanizing a layer offluororubber, which is mixed with a silica-type filler and containsvinylidene-fluoride units, and a layer of silicone rubber, whichcontains a silica-type filler and a silane-coupling agent that containsamino groups. Kokai 2003-214565 discloses a rubber hose having anintermediate layer of a silicone rubber that contains an adhesivecomponent and is placed between a fluororubber layer and asilicone-rubber layer. However, provision of the adhesive component inthe silicone rubber impairs its heat-resistant properties and handlingconditions and therefore limits application of the aforementionedlaminates. Furthermore, exposure of the laminate to hot environmentweakens bonding between the fluororubber layer and the silicone rubber.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a heat-curablesilicone rubber composition that makes it possible to obtain, in arubber laminate composed of a silicone-rubber layer and a rubber layerother than a silicone rubber, such a silicone-rubber layer thatpreserves strong bonding to the aforementioned rubber layer other thanthe silicone-rubber layer, even after exposure to high temperatures.

The heat-curable silicone rubber composition of the invention for arubber laminate composed of a silicone-rubber layer and a rubber layerof a material other than silicone comprises:

-   -   100 parts by mass of an alkenyl-containing        diorganopolysiloxane (A) which comprises:    -   50 to 99 mass % of an alkenyl-containing diorganopolysiloxane        (A1) that is capped at molecular terminals with        alkenyl-containing organosilyl groups, is free of alkenyl groups        in side molecular chains, and has a degree of polymerization in        the range of 2,500 to 100,000;    -   1 to 50 mass % of an alkenyl-containing diorganopolysiloxane        (A2) having two or more alkenyl groups in a side molecular chain        and having a degree of polymerization in the range of 2,500 to        100,000;    -   10 to 100 parts by mass of a fine silica powder (B) having        specific surface area in the range of 50 m²/g to 400 m²/g;    -   0.1 to 10 parts by mass of an organohydrogenpolysiloxane (C)        having in one molecule at least two silicon-bonded hydrogen        atoms; and    -   0.1 to 5 part by mass of an organic peroxide (D).

The rubber laminate of the present invention is obtained bysimultaneously cross-linking and curing a heat-curable fluororubbercomposition and a heat-curable silicone composition, both compositionsbeing in contact with each other during cross-linking;

-   -   the aforementioned heat-curable silicone rubber composition        comprising:    -   100 parts by mass of an alkenyl-containing        diorganopolysiloxane (A) that comprises:    -   50 to 99 mass % of an alkenyl-containing diorganopolysiloxane        (A1) that is capped at molecular terminals with        alkenyl-containing organosilyl groups, is free of alkenyl groups        in side molecular chains, and has a degree of polymerization in        the range of 2,500 to 100,000;    -   1 to 50 mass % of an alkenyl-containing diorganopolysiloxane        (A2) having two or more alkenyl groups in a side molecular chain        and having a degree of polymerization in the range of 2,500 to        100,000;    -   10 to 100 parts by mass of a fine silica powder (B) having        specific surface area in the range of 50 m²/g to 400 m²/g;    -   0.1 to 10 parts by mass of an organohydrogenpolysiloxane (C)        having in one molecule at least two silicon-bonded hydrogen        atoms; and    -   0.1 to 5 part by mass of an organic peroxide (D).

The heat-curable silicone rubber composition of the invention issuitable for forming a rubber laminate composed of strongly bondedlayers of a silicone-rubber and a rubber layer other than silicone, thelaminate being formed by subjecting both layers to cross-linking andcuring simultaneously while these layers are maintained in mutualcontact. In particular, the composition is suitable for forming a rubberlaminate that demonstrates good interlayer-bonding properties withrespect to a hard-to-bond fluororubber layer. The aforementioned rubberlaminate preserves strong bonding between the silicone-rubber layer anda layer of rubber other than silicone even after exposure to harshhigh-temperature environment at temperatures exceeding 200° C. Themethod of the invention is efficient in that it allows manufacturing ofthe aforementioned rubber laminate with high efficiency and underindustrial conditions.

BEST MODE FOR CARRYING OUT THE INVENTION

The alkenyl-containing diorganopolysiloxane (A) is one of the maincomponents of the heat-curable silicone rubber composition of theinvention. It comprises constituents (A1) and (A2) described below. Theweight ratio of (A1): (A2) ranges from 50:50 to 99:1 and shouldpreferably be in the range of 60:40 to 98:2. If constituent (A1) is usedin an amount which is too small, or if constituent (A2) is used inexcess, it will be difficult to provide sufficiently strong interlayerbonding in a rubber laminate obtained by simultaneously cross-linkingand curing the silicone-rubber composition of the invention and a layerof rubber other than silicone rubber when both layers are maintained inmutual contact. If constituent (A1) is used in an excessive amount andthe amount of constituent (A2) is too small, it will be difficult toprovide strong interlayer bonding after exposure of the rubber laminateto the effect of a high-temperature environment.

It is recommended to have component (A) with a linear molecularstructure, however, within the limits that are not detrimental toresilient properties in the product obtained by cross-linking and curingthe heat-curable silicone rubber of the invention, component (A) with apartially-branched molecular structure is also acceptable.

Constituent (A1) is an alkenyl group containing diorganopolysiloxanethat is capped at molecular terminals with alkenyl-containingorganosilyl groups, and is free of alkenyl groups in side molecularchains. This is an important constituent, which in combination with thebelow-described constituent (A2) and component (C), imparts strongbonding properties to a rubber laminate obtained by simultaneouslycross-linking and curing the silicone-rubber composition of theinvention and a layer of rubber other than silicon rubber, even afterexposure to high temperature environment. Constituent (A1) may comprisea diorganopolysiloxane capped at both molecular terminals withalkenyldiorganosilyl groups. Constituent (A1) is a gum-like substancethat has a degree of polymerization in the range of 2,500 to 100,000,preferably in the range of 3,000 to 20,000. If necessary, constituent(A 1) may comprise a combination of two or more appropriatediorganopolysiloxanes of the aforementioned type having differentmolecular structures and degrees of polymerization. Here, the degree ofpolymerization is a value determined from a polystyrene-referencednumber-average molecular weight measured by gel permeationchromatography (GPC).

Alkenyl groups of constituent (A1) may be exemplified by vinyl, allyl,butenyl, or hexenyl groups, of which vinyl groups are preferable fromthe cost viewpoint. Silicon-bonded groups other than alkenyl groups maybe exemplified by non-substituted or substituted monovalent hydrocarbongroups having 1 to 20 carbon atoms, preferably 1 to 8 carbon atoms. Suchgroups may be represented by methyl, ethyl, propyl, butyl, or similaralkyl groups; cyclohexyl, or similar cycloalkyl groups; phenyl, tolyl,or similar aryl groups, benzyl, β-phenylpropyl, or similar aralkylgroups; chloromethyl, trifluoropropyl, cyanoethyl, or similar groups ofthe aforementioned type wherein a part or all carbon-bonded hydrogenatoms are substituted with halogen atoms or cyano groups. Mostpreferable of the above groups are alkyl, in particular methyl groups,especially if more than 50 mole %, preferably more than 80 mole %, andmost preferably more than 95 mole % of silicon-bonded groups are methylgroups.

Constituent (A2) is a diorganopolysiloxane having at least two alkenylgroups in side molecular chains. Constituent (A2) is an importantconstituent, which in combination with constituent (A1) impartsexcellent interlayer bonding properties to a rubber laminate produced bysimultaneously cross-linking and curing the heat-curable silicone rubbercomposition and a rubber composition other than the silicone-rubbercomposition, when during cross-linking the aforementioned compositionsare maintained in mutual contact. Constituent (A2) is a gum-likesubstance that has a degree of polymerization in the range of 2,500 to100,000, preferably in the range of 3,000 to 20,000. Similar to theprevious case, here the degree of polymerization is a value determinedfrom a polystyrene-referenced number-average molecular weight measuredby gel permeation chromatography (GPC).

Alkenyl groups present in constituent (A2) may be exemplified by thesame appropriate groups that were mentioned above, of which vinyl groupsare preferable. From the viewpoint of improved balance between theinterlayer bonding properties with the aforementioned rubber layer otherthan the silicone layer and mechanical strength of the cross-linked bodyobtained by cross-linking and curing the aforementioned heat-curablesilicone rubber composition of the invention, it is recommended thatconstituent (A2) contain alkenyl groups in the amount of 0.4 to 1.8 mass%. In addition to side molecular chains, the alkenyl groups may alsoexist on molecular terminals. Furthermore, in addition to the alkenylgroups, this constituent may contain other silicon-bonded groups whichare the same as corresponding groups mentioned above, of whichpreferable are alkyl groups, in particular methyl groups. It isrecommended that more than 50 mole %, preferably more than 80 mole %,and most preferably more than 95 mole % of silicon-bonded groups bemethyl groups. Constituent (A2) may comprise a combination of two ormore of the aforementioned diorganopolysiloxanes that have differentmolecular structures, degrees of polymerization, contents of alkenylgroups, etc.

The fine silica powder that constitutes component (B) used in theheat-curable silicone rubber composition of the present invention isused for imparting excellent mechanical strength to the cured bodyobtained by cross-linking and curing the heat-curable silicone rubbercomposition of the invention. The aforementioned fine silica powder maybe represented by fumed silica powder or a similar dry-process silica;precipitated silica, or a similar wet-process silica; or theaforementioned silicas subjected to hydrophobic surface treatment withorganosi lane, hexaorganodisilazane, diorganopolysiloxane,diorganocyclopolysiloxane, or similar organosilicon compounds. The finesilica powder should have a diameter of particles equal to or less than50 μm. Furthermore, its specific surface area should be in the range of50 m²/g to 400 m²/g, preferably in the range of 100 m²/g to 400 m²/g,Component (B) should be used in an amount of 10 to 100 parts by mass per100 parts by mass of component (A). if component (B) is used in anamount less than 10 parts by mass, a body obtained after curing theheat-curable silicone rubber composition of the invention will haveinsufficient mechanical strength. If, on the other hand, the content ofcomponent (B) exceeds 100 parts by mass, this will impair compoundingthereof with component (A).

The organohydrogenpolysiloxane that constitutes component (C) containsin one molecule at least two silicon-bonded hydrogen atoms. This is animportant component that imparts strong interlayer bonding properties toa rubber laminate obtained by simultaneously cross-linking and curingthe silicone-rubber composition of the invention and a layer of rubberother than silicon rubber. Silicon-bonded groups other than hydrogenatoms can be exemplified by the same other groups as those mentionedwith regard to constituent (A1), preferable of which are alkyl groups,especially methyl groups. The organohydrogenpolysiloxane of component(C) may have a linear, partially branched, net-like, cyclic, or athree-dimensional molecular structure. This component may comprise asingle polymer, or a mixture of two or more polymers. There are nospecial restrictions with regard to viscosity oforganohydrogenpolysiloxane (C) at 25° C., but normally this componenthas a viscosity ranging from 0.5 to 50,000 mPa·s, preferably from 1 to10,000 mPa·s. Component (C) is used in the amount of 0.1 to 10 parts bymass per 100 parts by mass of component (A). Iforganohydrogenpolysiloxane (C) is used in the amount less than therecommended lower limit, the bonding force between the layers in therubber laminate obtained by simultaneously cross-linking and curing thesilicone-rubber composition of the invention and a layer of rubber otherthan silicone rubber when both layers are maintained in mutual contactwill be insufficient. If, on the other hand, the content of component(C) exceeds the recommended upper limit, this will impair eitherworkability of the heat-curable silicone rubber composition of theinvention or physical properties of a cured body obtained bycross-linking and curing the composition.

The organic peroxide that constitutes component (D) is used forcross-linking and curing the heat-curable silicone rubber composition ofthe invention. This component may comprise a conventional compound usedfor the same purpose. Specific examples of such compounds are thefollowing: benzoyl peroxide, tertiary butyl per-benzoate, orthomethylbenzoyl peroxide, paramethyl benozoyl peroxide, 1,1-bis(tertiary-butylperoxy) 3,3,5-trimethyl cyclohexane, 2,5-dimethyl-2,5-di(tertiary-butyl-peroxy) hexane, or 2,5-dimethyl-2,5-di (tertiary-butylperoxy) hexyne. These compounds are used individually or in combinationof two or more. The organic peroxide of component (D) is used in theamount of 0,1 to 5 parts by mass per 100 parts by mass of component (A).

Within the limits which do not contradict to the objects of theinvention, the heat-curable silicone rubber composition of the inventionmay be combined with various agents, such as diatomaceous earth, quartzpowder, calcium carbonate or similar extender; titanium oxide, carbonblack, red oxide, or similar pigments; rare-earth type oxides, ceriumlanolate, cerium fatty-acid salts, or similar heat-resistant agents;stearic acid, zinc stearate, calcium stearate, or similar fatty aids ortheir metal salts, or other mold-release agents.

The aforementioned rubber material other than the silicone rubber usedin the rubber laminate of the present invention is exemplified byfluororubber; acrylonitrile-butadiene copolymer, hydrogenatedacrylonitrile-butadiene copolymer, or a similar acrylonitrile rubber;acrylic rubber, a copolymer of ethylene and acrylic acid ester, acopolymer of vinyl acetate, ethylene, and acrylic acid ester; EPM, EPDM,or a similar ethylene-propylene type rubber. The fluororubber ispreferable.

There are no special restrictions with regard to the fluororubbersuitable for use in the rubber laminate of the present invention. Thepolymers of the following compounds are examples of the aforementionedfluororubber: vinylidene fluoride (VdF), hexafluoropropylene (HFP),pentafluoropropylene, trifluoroethylene, trifluorochloroethylene (CTFE),tetrafluoroethylene (TFE), vinylfluoride, perfluoro (methylvinylether),perfluoro (propylvinylidene), etc. Other examples may include compoundsthat can be used as a monomer copolymerizable with the aforementionedcompounds, such as acrylic acid esters or similar vinyl compounds,propylene or similar olefin compounds or diene compounds, as well ashalogenated vinyl compounds that contain chlorine, bromine, or iodine,or other copolymerized rubbers. Specific examples of such copolymers arethe following: a copolymer of VdF and HFP, a copolymer of VdF and TFE, acopolymer of VdF and CTFE, a trimer of TFE, propylene, and VdF, a trimerof TFE, HFP, and VdF, a copolymer of HFP, ethylene, and VdF, a copolymerof fluoro (alkylvinylether) and olefin (e.g., a copolymer of VdF, TFE,and perfluoro (alkylvinylether)), or a copolymer of THF and propylene.Most preferable of the above compounds are the trimer of TFE, propylene,and VdF, the trimer of TFE, HFP, and VdF, and the copolymer of VdF andHFP.

There are no special restrictions with regard to a method that can beused for cross-linking and curing the fluororubber, and appropriateconventional method can be used for this purpose. For example, this maybe peroxide-based curing by mixing with an organic peroxide and, ifnecessary, with a bifunctional vinyl monomer, or a similarcross-linking-assisting agent; polyol-based curing by mixing with2,2-bis (4-hydroxyphenyl) propane, or a similar polyol compound and, ifnecessary, with a quaternary ammonium salt, or a similar cross-linkingassistant; polyamine curing based on the use of hexamethylene diaminecarbamate; or polythiol curing based on the use of dimercaptodimethylether, or a similar sulfur-containing compound and, if necessary, of aquaternary ammonium salt or a similar cross-linking assistant. Mostpreferable from the viewpoint of imparting excellent heat-resistantproperties are the peroxide-based curing method and the polyol-basedcuring method.

The fluororubber can be combined with other components such as asilica-type filler, a plasticizer such as a phthalic-acid derivative,adipic acid derivative, sebacic acid derivative, a softener such aslubricating oil, process oil, castor oil, antioxidants such as phenylenediamines, phosphates, quinolines, cresols, phenols, dithiocarbamatemetal salts, etc.

The rubber laminate of the present invention is produced bysimultaneously heating and thus cross-linking and curing theheat-curable silicone composition of the present invention and aheat-curable rubber composition other than silicone composition, e.g., afluororubber composition or the like which is compounded with a curingagent, both compositions being maintained in mutual contact duringcuring. There are no special restrictions with regard to the curingconditions but it may be recommended to conduct this process under apressure in the range of 2 to 100 kg/cm² and at a temperature rangingfrom 100 to 200° C. Molding can be carried out by a compression-moldingmethod; an injection-molding method; and extruding method which theheat-curable rubber composition of the invention and the rubbercomposition other than the silicone composition is continuously extrudedwith an extruder and the rubber laminate is cured, e.c. by steamheating. If necessary, after molding the product can be subjected tosecondary vulcanization by heat-treating the obtained rubber laminate.

There are no special restrictions with regard to the form of the rubberlaminate of the invention. For example, this can be a two-layerlaminate, a three-layer laminate, or a laminate having more than threelayers, or a multiple-layer product having fiber-reinforces layers.Specific examples are the following: a rubber laminate having the innerlayer made from a fluororubber or another rubber different from siliconerubber and the external layer made from the silicone rubber; a rubberlaminate having the inner layer made from a fluororubber or anotherrubber different from silicone rubber, an intermediate layer made fromthe silicone rubber, and the external layer made from a fluororubber oranother rubber different from silicone rubber; or a rubber laminatehaving the inner layer made from a fluororubber or another rubberdifferent from silicone rubber, an intermediate layer made from thesilicone rubber, and the external layer made from a fiber-reinforcedlayer.

PRACTICAL EXAMPLES

The invention will be further described by way of practical andcomparative examples, which, however, should not be construed aslimiting the scope of the invention.

[Preparation of Heat-Curable Silicone Rubber Composition]

A kneader mixer was loaded with an organopolysiloxane, adimethylpolysiloxane capped at both molecular terminals with hydroxylgroups, and silica in the proportions shown in Table 1. The componentswere mixed and kneaded for 30 min. at 30° C. and then for 60 min. at170° C., whereby a silicone- rubber composition was produced. Inproportions shown in Table 1, the obtained composition was compoundedwith an organohydrogenpolysiloxane and dicumylperoxide, whereby aheat-curable silicone rubber composition was produced.

[Preparation of Heat-Curable Huororubber Compositions 1, 2, and 3]

100 parts by mass of DAI-EL G-902 (the product of Daikin Industries,Ltd.) were combined with 2.0 parts by mass of PERHEXA® 25B(2,5-dimethyl-2-di(t-butylperoxy) hexane (the product of NOF Co.),whereby heat-curable fluororubber composition 1 was produced.Furthermore, 100 parts by mass of Dyneon FLS-2650 (the product of 3MCo., Inc.) were combined with 2.0 parts by mass of PERHEXA®(2,5-dimethyl-2-di(t-butylperoxy) hexane (the product of NOF Co.),whereby heat-curable fluororubber composition 2 was produced. Similarly,100 parts by mass of polyol-curable DAI-EL G-558 (compounded withPolyol) (the product of Daikin Industries, Ltd.) were compounded with 3parts by mass of magnesium oxide and 6 parts by mass of calciumhydroxide, whereby heat-curable fluororubber composition 3 was produced.

[Preparation of Rubber Laminate]

A non-cross-linked sheet having a thickness of 0.5 mm was produced bykneading a heat-curable fluororubber composition in a two roll mill withheating at 60° C. A non-cross-linked sheet having a thickness of 3 mmwas produced by kneading a heat-curable silicone rubber composition in atwo roll mill with roll temperature of 30° C. Following this, the sheetof the non-cross-linked fluororubber sheet was wound onto an aluminumcylinder having a diameter of 150 mm. The sheet of the non-cross-linkedsilicone rubber was wound onto the first-mentioned sheet and then acloth was wound on the sheet of the non-cross-linked silicone rubber tosecure those rubber sheets to the cylinder, and then the unit was heatedfor 20 min. at 150° C. in a steam autoclave. The unit treated in theabove-described manner was removed from the autoclave, the cured bodywas disconnected from the cylinder and heated in an oven for 12 hours at200° C., whereby a rubber laminate was produced.

[Evaluation of Bonding Strength]

The rubber laminate produced by the method described above was retainedfor 24 hours at room temperature and then was cut into 25 mm-wideribbons which were used for evaluating initial bonding strength betweenthe silicone-rubber layer and the fluororubber layer by a T-type peelmethod. Furthermore, the rubber laminate obtained by the aforementionedmethod was for the second time retained in an oven, but for 72 hours at220° C., and, after the above-mentioned ageing was completed, thelaminate was evaluated with regard to the bonding strength by a T-typepeel test. The bonding strength between the silicone-rubber layer andthe fluororubber layer was evaluated as excellent when the peeling testshowed high resistance to peeling and when cohesive failure wasobserved. The bonding strength was evaluate as low when peeling occurredwithout resistance with separation over the interface, and the testresults were qualified as non-applicable (NA) when during the T-typepeel test the silicone-rubber layer was ruptured.

[Practical Examples 1 to 5 and Comparative Examples 1 to 5]

Properties of the rubber laminate produced by the above-described methodfrom the heat-curable silicone rubber composition and the heat-curablefluoro-rubber composition were studied on the basis of bonding strengthbetween the silicone and fluororubber layers prior to and after ageing.The results are shown in Table 1.

TABLE 1 Practical Examples Comparative Examples 1 2 3 4 5 1 2 3 4 5 A1Organopolysiloxane a1 95 90 60 95 90 100 40 — 95 95 A2Organopolysiloxane a2 5 — — 5 — — — — 5 5 A2 Organopolysiloxane a3 — 1040 — 10 — 60 — — — A2 Organopolysiloxane a4 — — — — — — — 100 — — BSilica b1 36 36 36 — — 36 36 36 36 — B Silica b2 — — — 36 36 — — — — 36Dimethylpolysiloxane 10 10 10 1.5 1.5 10 10 10 10 1.5 having bothmolecular terminals capped with hydroxyl groups C Organohydrogen- 2.22.2 2.2 2.1 2.1 2.2 2.2 2.2 — — polysiloxane c1 D Dicumyl peroxide 1.51.5 1.5 1.4 1.4 1.5 1.5 1.5 1.5 1.4 Bonding strength of heat- ExcellentPoor NA Excellent curable fluororubber composition 1 prior to ageingBonding strength of heat- Excellent Poor NA Poor curable fluororubbercomposition 1 after ageing Bonding strength of heat- Excellent Poor NAPoor Excellent curable fluororubber composition 2 prior to ageingBonding strength of heat- Excellent Poor NA Poor curable fluororubbercomposition 2 after ageing Bonding strength of heat- Excellent Poor NAExcellent curable fluororubber composition 3 prior to ageing Bondingstrength of heat- Excellent Poor NA Poor curable fluororubbercomposition 3 after ageing

Designations used in Table 1 have the following meanings:

Component (A) Constituent (A1)

-   Organopolysiloxane a1: dimethylpolysiloxane gum capped at both    molecular terminals with vinyldimethylsilyl groups and having degree    of polymerization of about 5,000 Constituent (A2)-   Organopolysiloxane a2: gum copolymer of methylvinylsiloxane and    dimethylpolysiloxane capped at both molecular terminals with    hydroxyl groups and having degree of polymerization of about 4,000    (vinyl-group content: 1.45 mass %)-   Organopolysiloxane a3: gum copolymer of methylvinylsiloxane and    dimethylpolysiloxane capped at both molecular terminals with    dimethylvinylsilyl groups and having degree of polymerization of    about 5,000 (vinyl-group content: 0.72 mass %)-   Organopolysiloxane a4: gum copolymer of methylvinylsiloxane and    dimethylpolysiloxane capped at both molecular terminals with    dimethylvinylsilyl groups and having degree of polymerization of    about 5,000 (vinyl-group content: 0.07 mass %)

Component (B)

-   Silica b1: fumed silica with specific surface area of 200 m²/g-   Silica b2: fumed silica having specific surface area of 160 m²/g and    hydrophobically surface treated with octamethyl-cyclotetrasiloxane

Component (C)

-   Organohydrogenpolysiloxane C1: copolymer of methylhydrogensiloxane    and dimethylsiloxane having viscosity of 15 mPa·s at 25° C. and    represented by the following average molecular formula: Me₃SiO    (Me2SiO)₁₂ (MeHSiO)₁₅ SiMe₃

Component (D)

-   Dicumyl peroxide (used as a peroxide type curing agent)

Other Components

-   Dimethylpolysiloxane capped at both molecular terminals with    hydroxyl groups: dimethylpolysiloxane capped at both molecular    terminals with hydroxyl groups and having viscosity of 40 in Pa·s at    25° C.; used as a treatment agent for silica (B)

INDUSTRIAL APPLICABILITY

The rubber laminate of the present invention is characterized by strongbonding between the silicone rubber layer and the fluororubber layer, aswell as by excellent properties such as resistance to heat, resistanceto oil, resistance to fuel oil, resistance to LLC [long life coolant],resistance to steam, and weather-proof properties. In view of the abovethe aforementioned rubber laminate may be used for manufacturinggaskets, non-contact or contact-type packings, bellows, or similarsealing members (which in the automotive industry can be used as sealingelements for engine casings, main-drive systems, valve systems,lubrication and cooling systems, fuel systems, suction-exhaust systems;transmissions of chassis and drive systems, steering systems, brakingsystems; basic parts of electrical equipment, electrical parts ofcontrol systems, parts of electrical installations, etc.); valves, tireframes; fuel-supply hoses, oil-supply hoses, gas-supply hoses,brake-fluid supply hoses, steam-supply hoses, chemically resistivehoses, or other hoses or tubes of the aforementioned type; appropriateuse in electric wirings, etc. The rubber laminate of the invention mayfind application also in equipment of chemical plants, food industry,nuclear plants, or in general industrial equipment. In addition to theuse in automotive industry, the rubber laminate may find application inother transportation means such as ships and aircrafts.

1. A heat-curable silicone rubber composition for a rubber laminatecomposed of a silicone-rubber layer and a rubber layer of a materialother than silicone, the composition comprising: 100 parts by mass of analkenyl-containing diorganopolysiloxane (A) which comprises: 50 to 99mass % of an alkenyl-containing diorganopolysiloxane (A1) that is cappedat molecular terminals with alkenyl-containing organosilyl groups, isfree of alkenyl groups in side molecular chains, and has a degree ofpolymerization in the range of 2,500 to 100,000; 1 to 50 mass % of analkenyl-containing diorganopolysiloxane (A2) having two or more alkenylgroups in side molecular chains and having a degree of polymerization inthe range of 2,500 to 100,000; 10 to 100 parts by mass of a fine silicapowder (B) having specific surface area in the range of 50 m²/g to 400m²/g; 0.1 to 10 parts by mass of an organohydrogenpolysiloxane (C)having in one molecule at least two silicon-bonded hydrogen atoms; and0.1 to 5 part by mass of an organic peroxide (D).
 2. The heat-curablesilicone rubber composition for a rubber laminate according to claim 1,wherein the rubber laminate comprises a silicone-rubber layer and afluororubber layer.
 3. The heat-curable silicone rubber composition fora rubber laminate according to claim 1, wherein the content of alkenylgroups in constituent (A2) ranges from 0.4 to 1.8 mass %.
 4. (canceled)5. (canceled)
 6. The heat-curable silicone rubber composition for arubber laminate according to claim 2, wherein the content of alkenylgroups in constituent (A2) ranges from 0.4 to 1.8 mass %.
 7. Theheat-curable silicone rubber composition for a rubber laminate accordingto claim 1, wherein the degree of polymerization of constituent (A1) isin the range of 3,000 to 20,000.
 8. The heat-curable silicone rubbercomposition for a rubber laminate according to claim 1, wherein thedegree of polymerization of constituent (A2) is in the range of 3,000 to20,000.
 9. The heat-curable silicone rubber composition for a rubberlaminate according to claim 1, wherein the alkenyl groups of constituent(A1) are vinyl.
 10. The heat-curable silicone rubber composition for arubber laminate according to claim 3, wherein, in addition to thealkenyl groups, constituent (A1) contains other silicon-bonded groupswhich are alkyl groups.
 11. The heat-curable silicone rubber compositionfor a rubber laminate according to claim 10, wherein more than 50 mole %of silicon-bonded groups in constituent (A1) are the alkyl groups. 12.The heat-curable silicone rubber composition for a rubber laminateaccording to claim 11, wherein the alkyl groups are methyl groups. 13.The heat-curable silicone rubber composition for a rubber laminateaccording to claim 3, wherein, in addition to the alkenyl groups,constituent (A2) contains other silicon-bonded groups which are alkylgroups.
 14. The heat-curable silicone rubber composition for a rubberlaminate according to claim 13, wherein more than 50 mole % ofsilicon-bonded groups in constituent (A2) are the alkyl groups.
 15. Theheat-curable silicone rubber composition for a rubber laminate accordingto claim 14, wherein the alkyl groups are methyl groups.
 16. Theheat-curable silicone rubber composition for a rubber laminate accordingto claim 1, wherein the fine silica powder has a specific surface areain the range of 100 m²/g to 400 m²/g.
 17. A heat-curable silicone rubbercomposition for a rubber laminate composed of a silicone-rubber layerand a rubber layer of a material other than silicone, the compositioncomprising: 100 parts by mass of an alkenyl-containingdiorganopolysiloxane (A) which comprises: 60 to 98 mass % of analkenyl-containing diorganopolysiloxane (A1) that is capped at molecularterminals with alkenyl-containing organosilyl groups, is free of alkenylgroups in side molecular chains, and has a degree of polymerization inthe range of 2,500 to 100,000; 2 to 40 mass % of an alkenyl-containingdiorganopolysiloxane (A2) having two or more alkenyl groups in sidemolecular chains and having a degree of polymerization in the range of2,500 to 100,000; 10 to 100 parts by mass of a fine silica powder (B)having specific surface area in the range of 50 m²/g to 400 m²/g; 0.1 to10 parts by mass of an organohydrogenpolysiloxane (C) having in onemolecule at least two silicon-bonded hydrogen atoms; and 0.1 to 5 partby mass of an organic peroxide (D).